1. Field of the Invention
The present invention relates to machines used for stuffing product such as sausage and more particularly to a safety closure for such a machine.
2. Description of the Prior Art
It is well known in the art, as disclosed in U.S. Pat. No. 1,062,989 to Naegelen for example, to provide a machine for stuffing plastic product, such as ground sausage, having a piston located in an internal chamber which is driven against the plastic product by introduction of a pressurized medium in order to force the plastic product through a nozzle and into a casing.
Such machines have a cover removable for access to an internal chamber for loading of the product. It is also required, particularly where meat products are involved, that access be available for thorough cleaning and therefore highly desirable that such access be simplified.
However, militating against easy access to the internal chamber is the fact that the forces required to drive such product are frequently quite large, particularly where products of lesser fluidity are involved. Prior art stuffing machines lacking safety measures were subject to explosive ejection of the pistons resulting in injuries. Various methods for restricting such explosive ejection are known in the art. In the Naegelen U.S. Pat. (No. 1,062,989), a hinged cover is locked at an outer periphery through locking nuts carried on tie rods pivotally attached to the stuffer. Such a cover construction provides only limited safety relief because, as the Naegelen disclosure recognizes, the cover could be closed and pressure applied to the machine by an operator who had neglected to secure the lock nuts, resulting in explosive discharge. The Naegelen Patent discloses the provision of a relief valve triggered by an upwardly moving piston as a solution to the prospected unintentional unsecured cover. This solution however, involving a system interaction of trigger, lever, spring loaded valve stem and valve seat, is not failsafe and even when operational does not provide a stop for an already moving piston but merely lessens the pressure in the chamber behind the piston such that contact with an unsecured cover could still result.
Other systems for locking a cover of a stuffing machine are known, such as disclosed in U.S. Pat. No. 1,465,655 to Schmidt, in which a cover is restrained against opening by an external hinged yoke pivoted into position over a closed cover. However, the use of external restraints does not provide for a stop between the piston and the cover. The cover of the Schmidt device can be closed without the yoke being secured such that an operator could mistakenly apply pressure to an unsecured machine resulting in undesirable contact between the piston and an unlocked cover. The Schmidt disclosure includes the teaching of a triggered valve system for releasing pressure behind an upwardly driven piston prior to contact between piston and cover, similar to that found in Naegelen, and subject to the same limitations.
Accordingly, it is an object of the present invention to provide a safety closure for a product stuffing machine which allows for ready access to an internal product chamber of the machine for loading of product and for removal and necessary cleaning of surfaces which come in contact with the product.
It is a further object of the invention to provide a safety closure for a product stuffing machine in which a stopping feature to control a driven piston is direct and reliable and not dependent on system interactions for an indirect solution.
It is still a further object of the present invention to provide an improved product stuffing machine having as a safety feature the interaction of a safety stop with other machine components to reduce the likelihood of inadvertent pressurization with a closed but unsecured machine thereby reducing reliance on operator diligence.